The invention relates generally to polymers and methods for preparing and using the polymers. In particular, the invention relates to copolymers, methods for preparing the copolymers, and methods for using the copolymers to remove heavy metals from aqueous solutions.
Heavy metal pollution is an existing and growing worldwide problem. For example, waste water issuing from waste treatment facilities, from the chlor-alkali industry, from the metal finishing industry, and from certain municipal landfills often presents a metal contamination problem. Similarly, the metal content of water exiting both or either of functional and abandoned mines is a significant environmental issue in geographical areas with a mining industry.
Different treatment techniques have been developed to remove either or both dissolved and suspended heavy metal ions from industrial waters and wastewaters. One common practice is to precipitate the bulk of the heavy metal contaminant as its metal hydroxide. Metal ions such as copper and lead are easily precipitated in this way, but the minimum concentration that can be obtained is limited by the finite solubility of the hydroxide complexes. The resulting effluent from the hydroxide precipitation may be treated with a metal scavenging agent to remove any trace metal contaminants to meet discharge regulations. These agents may be precipitants, adsorbents, or metal specific ion exchange resins. The metal scavenger precipitants may also be effective when added in the same step as the hydroxide precipitation. Typical compounds utilized as precipitating scavenging agents include sulfides, (thio)carbonates, alkyl dithiocarbamates, mercaptans, and polydithiocarbamates.
The prior art scavenging agents have limitations. The metal thiocarbonates, sulfides, mercaptans, and thiocarbamates form fine flocs which are not conducive to settling and typically require the use of a flocculation agent. The metal thiocarbonates, sulfides, mercaptans, and thiocarbamates are unstable over time and under certain pH conditions because the thiocarbonates, sulfides, mercaptans, and thiocarbamates lack sufficient binding sites for heavy metal ions. Such unstable precipitates may release bound metal back into the environment, thereby proving unsatisfactory as treatment or remediation agents. Prior art polydithiocarbamates are characterized as having limited water solubility, which limits the possible degree of functionalization. In addition, a number of the prior art scavenging agents are themselves very toxic and care must be taken to ensure that they are not present in the discharged wastewater.
There exists a need, therefore, for a new material to remove heavy metals from aqueous solutions. It is desirable that this material is less toxic and forms larger, and faster settling precipitates than the prior art compounds which remain stable over a range of environmental conditions and over extended periods of time. It is also desirable that this material is water-soluble so it can be utilized in existing clarification facilities, avoiding the need for capital investment in resin-bed apparatus or other specialized equipment. It is also desirable that this material can be prepared easily and cheaply, and has an adequate molecular weight, chemical stability, and high affinity for one or more heavy metal ions.